The biomechanical mechanism of invisible appliance in pushing the second molar backwards

Objective To research the biomechanical mechanism of the invisible appliance technique in the process of pushing the molar backwards. Methods A numerical model of volunteer was formed from sequential computed tomography (CT). Scan images was taken at 0.5 mm intervals by using Mimics, Solidworfs and Abques software. The three dimensional finite element including alveolar bone, upper denture, pericementum and bracketless appliance were established. The research was designed for three groups , pushing backwards 0.2 mm. Results The max stress was in the periodontal membrane of the distal surface of the root of the palate of the maxillary second molar and the palatal surface of the root of the palate of the maxillary first molar .The equivalent stress is concentrated at 7.5-10 Kpa. In the second, the stress of the periodontal membrane of the upper incisor and upper canines were mainly concentrated in 5-7.5 Kpa . Then, for lateral incisors and maxillary second premolar, the equivalent stress was mainly concentrated in 2.5-5 Kpa. Conclusions The Invisalign technique pushing the molar backwards, the max stress is the second molar, followed by maxillary first molar, followed by incisors in the upper jaw, and then followed by canines .Later incisors and premolars are less stressed. Before orthodontics, the thickness of the lip bone should be evaluated. In addition, the thickness of the lip bone should be prevented from being absorbed by protrusion of anterior teeth, and the class II elastic should be used timely. Key words: push the molar backwards; invisible appliance; finite element analysis